\begin{tikzpicture}
    \pgfmathsetmacro{\R}{1.5}
    \tkzDefPoints{0/0/O}
    \tkzDefPoint(230:\R){A}
    \tkzDefPoint(310:\R){B}
    \tkzDefLine[altitude](A,O,B)  \tkzGetPoint{D}
    \tkzInterLC(O,D)(O,A)  \tkzGetSecondPoint{C}

    \tkzDrawCircle[very thick](O,A)
    \tkzDrawSegments(A,B  O,C  A,C)
    \tkzDrawSegments[dashed](O,A  O,B)
    \tkzDrawPoint(O)
    \tkzMarkRightAngle[size=.2](B,D,O)
    \tkzLabelSegment[above, xshift=-.2em](O,A){$R$}
    \tkzLabelPoints[above](O)
    \tkzLabelPoints[left=.2em](A)
    \tkzLabelPoints[right=.2em](B)
    \tkzLabelPoints[below](C)
    \tkzLabelPoints[above, xshift=.5em, yshift=.3em](D)
\end{tikzpicture}

